Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

086
FXUS63 KLOT 211123
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
623 AM CDT Thu May 21 2026

.KEY MESSAGES...

- Showers likely late Friday into Friday night, especially
  across our south/southeast portions of the forecast area.

- Spotty shower chances at times during the extended holiday
  weekend, though many dry hours expected.

- Return to somewhat above average temperatures expected next
  week, though cooler temperatures expected near the lake.

&&

.DISCUSSION...
Issued at 246 AM CDT Thu May 21 2026

Early morning surface analysis places 1030 mb high pressure
over the northern Great Lakes. This will maintain breezy
northeast to easterly surface winds, reinforcing a cool/dry low
level air mass across the forecast area as the high slowly
drifts east through Friday. Aloft, the upper pattern generally
features troughing across the western CONUS, with west-
southwesterly upper level flow from the Plains to the Great
Lakes. Within this flow, a a subtle mid-level short wave was
evident in GOES vapor imagery tracking east-northeast from
NE/KS. A few high-based convective showers (isolated
thunderstorms earlier) were noted from northeast KS into far
southwest IA in association with this wave, along the northern
periphery of a 7-7.5 C/km mid-level lapse rate/weak MUCAPE
plume. Several CAMs indicate some spotty precip potential into
WI/far northern IL as the wave tracks into our region later this
morning, though with such dry low-levels and high convective
bases (~10 kft) chances of actual measurable rain appears quite
low. Have added a slight chance (<15%) pop roughly north of a
Sterling to Waukegan line for sprinkles from after daybreak
through late morning for this potential. Otherwise, dry
conditions are expected today through Friday morning. Breezy
northeast winds with gusts 20-25 mph will keep temperatures on
the cool side again today, with highs from the 50s along Lake
Michigan to the low-mid 60s farther inland and some upper 60s
south of the I-80 corridor. Those breezy winds will also
continue to produce hazardous swimming conditions at Lake
Michigan beaches through this morning, before easing a bit this
afternoon.

Much farther to our west, a jet-streak digging southeast across
the northern Rockies is progged to carve out a stronger short
wave across the Plains Friday morning, before lifting northeast
across the upper Midwest late Friday/Friday night. Meanwhile, a
weaker southern stream wave is forecast to lift northeast from
TX into the lower OH Valley with a corresponding surface low
which tracks north of the Ohio River. Guidance has struggled a
bit with the degree (if any) of phasing between these two
disturbances, as well as the resulting rainfall footprint across
our area especially Friday night. Global ensembles generally
favor our south/southeast half of the forecast area for highest
rain chances, with the CMCE and EPS (to a lesser extent) still
producing 60-100% pops, with the NBM blend on the higher end of
the spectrum. There is a play however where particularly our
northwest half of the cwa ends up with little/no precipitation
during this time, and have limited NBM pops some there. Thunder
potential still appears fairly low, with only the Canadian GEM
guidance spreading MUCAPE into our southeastern cwa Friday
night.

Scattered showers may linger into early Saturday morning as the
main short wave trough axis shifts northeast across the area.
While we remain beneath the southern periphery of the larger
scale upper trough, forcing for precipitation during the day
appears nebulous and weak subsidence behind the departing
morning wave may support many dry daytime hours. Shower chances
do look to increase from the west late in the day/evening
however, as guidance depicts another mid-level short wave
rounding the base of the upper trough. The pattern remains
unsettled Sunday into Monday, as a series of weak waves ripple
through somewhat less amplified westerly flow aloft. Ensemble
QPF progs generally indicate Sunday afternoon may be favored for
a somewhat higher shower/thunderstorm threat, though overall
weak surface features and lack of significant deep moisture
lends to low confidence in any significant precip coverage
through the end of the holiday weekend. There remains decent
agreement in a continued gradual warmup (albeit still with some
lake cooling) from Saturday into mid-next week with daytime
highs in the 70s.

Ratzer

&&

.AVIATION /12Z TAFS THROUGH 18Z FRIDAY/...
Issued at 623 AM CDT Thu May 21 2026

Forecast concerns for the terminals...

- Breezy east-northeast winds this afternoon with gusts around
  25 kts.

- Non-zero chance (10-15%) for sprinkles light showers at RFD
  this morning and at all terminals Friday morning.


A broad surface high continues to reside over the northern Great
Lakes which will promote generally quiet weather conditions for
this TAF period. However, there is a weak disturbance lifting
across IA this morning which has lead to some sprinkles and
light showers at times. While these showers should wane as they
encounter the drier air over northwest IL, some of the deeper
cores noted on radar have given sufficient confidence to justify
adding a PROB30 to RFD for light showers for a couple of hours
this morning. Otherwise, VFR conditions are expected through the
TAF period. There is another low chance (10-15%) for some
isolated showers/sprinkles Friday morning areawide, but given
the modest forcing confidence is too low for any formal TAF
mention at this time.

Wind wise, directions remain east-northeastly through the
period. Speeds will increase through this afternoon with gusts
peaking around 25 kts, especially at the Chicago area terminals,
this afternoon. Gusts will subside this evening and remain
around 7-10 kts overnight into Friday morning.

Yack

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement through Saturday afternoon for ILZ006-
     ILZ103-ILZ104.

IN...Beach Hazards Statement through late tonight for INZ001.

     Beach Hazards Statement through this evening for INZ002.

LM...Small Craft Advisory until 1 PM CDT this afternoon for the IL
     nearshore waters.

     Small Craft Advisory until 7 AM CDT this morning for the IN
     nearshore waters.

&&

$$

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